Direct Air Capture of CO2 faces a 'thermodynamic wall' that prevents it from ever becoming cheap enough to save the planet.
April 1, 2026
Original Paper
No Joint Descent: Geometric Constraints on Cyclic Atmospheric CO2 Removal. The Thermodynamic Wall That Learning Curves Cannot Cross
SSRN · 6502405
The Takeaway
Unlike solar panels or batteries, the cost of sucking CO2 out of the air is limited by fundamental physics rather than just engineering. Because CO2 is so diluted in the atmosphere, the material and energy requirements create a hard price floor—likely over $1,000 per ton—that prevents it from following a typical 'learning curve' to low costs.
From the abstract
Atmospheric CO2 removal (termed DAC, DACCS, and others) lacks an agreed thermodynamic baseline, product specification, or cycle definition. Cost projections assume learning-curve behavior; we show feasibility is governed by a geometric constraint at the 400 ppm CO2 inlet concentration. The Second-Law penalty decomposes into three orthogonal irreversibility domains—thermal, masstransfer, and mechanical— which multiply to yield k2L > 4. Applied to adsorption-based systems, material constraints cre